摘要:

AbstractSymmetrical polyester‐aluminum‐polyester laminates are prepared using poly(ethylene terephthalate) film subjected to a glow discharge pretreatment. Extremely high peel energies (several hundred J m−2) are achieved, and the fracture path is principally cohesive: the laminate performance thus fully exploits the bulk mechanical properties of the PET. The peel surface exhibits extensive plasticity on a scale of tens of microns, with finer ductile tearing on a scale of order 1 μm. The mechanism of peel propagation and energy dissipation is discussed with regard to the optimisation of peel st

ISSN:0021-8995    

DOI:10.1002/app.1988.070350201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe average diad concentrations of methyl methacrylate (MMA) unit,P2{MiMj}, of the title terpolymer prepared by radical polymerization with various conversions were studied by1H‐NMR measurements. Several methoxy proton peaks of MMA resolved by the diamagnetic shielding effects of styrene were assigned to the individual microstructures of MMA‐centered triads. TheP2{MiMj} were determined from these peak ratios according to the terminal copolymerization model and the Ham's assumption of statistical simplification for a multicomponent copolymer (P2{MiMj} =P2{MjMi}), The observed values,P2{MiMj}, agreed with the values calculated from the monomer reactivity ratios for each conversions, and agreement with the copolymerization theory was evid

ISSN:0021-8995    

DOI:10.1002/app.1988.070350202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effects of sequence distribution on the glass transition temperature (Tg) of the title terpolymers prepared by radical polymerization were studied.Tgwas examined by thermomechanical analysis. The average diad concentrations, as estimation of sequence distributions were calculated from monomer reactivity ratios. A modified Gibbs–Dimarzio equation for binary copolymers was extended to terpolymers to explain the relation between observedTgand average diad concentrations. The observedTgshowed good agreement with the calculated values determined by the extended equatio

ISSN:0021-8995    

DOI:10.1002/app.1988.070350203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractHigh activity α‐olefin polymerization catalysts are generally obtained by mixing MgCl2‐supported TiCl4(MgCl2/TiCl4) with an aluminum trialkyl cocatalyst. Surprisingly, AlEt2Cl, which is the preferred cocatalyst in polymerizations employing nonsupported Ti compounds, is a poor cocatalyst when used with MgCl2/TiCl4. It was found that in propylene and 1‐butene polymerizations, using different MgCl2/TiCl4catalysts, the cocatalyst activity of AlEt2Cl can be greatly improved by the addition of a magnesium or lithium alkyl. The mixed metal alkyl obtained from AlEt2Cl and MgBu2is a particularly effective cocatalyst always yielding more polymer, of about the same stereospecificity, than the conventional aluminum trialkyls. The exact nature of the mixed metal alkyl cocatalysts is not known, but the available evidence argues against in situ aluminum trialkyl formation resulting from the alkylation of AlEt2Cl by the second metal

ISSN:0021-8995    

DOI:10.1002/app.1988.070350204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractStudies on tensile strength of polybutadiene (BR) and ethylene–propylene diene rubber (EPDM) having a wide range of flaw sizes have been carried out under both normal and aging conditions. A similar study has been done for a solid propellant rocket insulator compound, based on EPDM. The morphology of tensile fracture surface has also been reported in each case in order to understand the mechanism of rupture. Unlike NR, EPDM, and BR gum vulcanizates, both unaged and aged, show no critical cut length (lc).lcmay be defined as the cut length at which the strength decreases abruptly (sometimes there is a drop of a factor of 3 or more, atlc). However, the insulator compound, based on EPDM, exhibits a definitelcin the region of 1.5–1.7 mm. This arises because of anisotropic effect of asbestos fibers. Scanning electron microscopic studies show that the mechanisms of rupture of EPDM and BR gum vulcanizates are similar throughout the whole range of precuts. It occurs through a tearing process originated from the given precut at the center of the samples. A quantitative relation between tensile strength and distance between crack lines/tear lines has also been found. Though insulator compound shows a definitelc, similar fracture surface has been observed over the entire range of flaw si

ISSN:0021-8995    

DOI:10.1002/app.1988.070350205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractIt is shown how the global deformation mechanism in filler‐loaded vulcanizates were modified by additional filler‐to‐matrix bonds. A quantitative description is given in terms of an extended van der Waals treatment including the formulation of a reduced mechanical equation of state. An interpretation of the Mullins softening is pres

ISSN:0021-8995    

DOI:10.1002/app.1988.070350206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractDevelopment of crystalline structure during the tubular film blowing of low‐density polyethylene was investigated, using wide‐angle X‐ray diffraction technique, low‐angle light scattering, and scanning electron microscopy. In the study, commercial grades of both high‐pressure low‐density polyethylene (HP‐LDPE) and low‐pressure low‐density polyethylene (LP‐LDPE) (also, commonly referred to as linear low‐density polyethylene, LLDPE) were used. The applied stresses at the freeze line were determined using theoretical expressions derived in an earlier publication [C. D. Han and T. H. Kwack,J. Appl. Polym. Sci.,28, 3399 (1983)]. The applied stresses,S11FandS33F, at and above the freeze line in the machine and transverse directions were expressed in terms of the tension at the take‐up device, take‐up ratio, blow‐up ratio, and the pressure difference across the film of the bubble. These applied stresses were used to interpret the crystalline axes' orientation in the tubular blown films. It was found that the magnitude ofS11Fis an important process parameter for the crystalline axes' orientation and that the biaxial stress ratio (S11F/S33F) appears to be a determining factor in the distribution of fibrillous nuclei and crystalline texture,

ISSN:0021-8995    

DOI:10.1002/app.1988.070350207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe photopolymerizations of vinyl trifluoroacetate (VTFAc), vinyl acetate (VAc), and methyl methacrylate (MMA) using the initiation system benzophenone–tetrahydrofuran were studied at low temperatures. At −78°C the rate of polymerization of VTFAc was higher than that of VAc, while MMA, which was solidified, did not polymerize. After melting the irradiated solid mixture the polymerization occurred at 4°C. The photoinduced polymerization of VTFAc occurred in the presence of butylaldehyde or isobutylaldehyde at −70°C. The degrees of polymerization and syndiotacticities of the polymers prepared were inve

ISSN:0021-8995    

DOI:10.1002/app.1988.070350208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractIn an electron beam (EB) polymerization of a urethane‐acrylate prepolymer, the polymerization temperature greatly affected the structure and properties of the resulting gel film. Urethaneacrylate, which was synthesized by the reaction of poly(butylene adipate)diol, 4,4′‐diphenylmethane diisocyanate, and 2‐hydroxyethyl acrylate, was used as a prepolymer. The prepolymer was semicrystalline and showed a melting point in the region of 50–60°C. The maximum polymerization rate of the prepolymer was obtained when the prepolymer film was irradiated in the temperature range of 25–40°C. EB polymerization below the melting point (Tm) of the prepolymer produced semicrystalline polyurethane‐acrylate gel films with a spherulitic texture. On the other hand, EB polymerization above theTmdestroyed the crystalline phase of the prepolymer to give transparent gel films. The gel film cured below theTmhad higher stress at yield, Young's modulus, and tensile strength than those cured above theTm. Such temperature effects are attributed to whether or not the EB polymerization proceeds with retention of crystalline structure of

ISSN:0021-8995    

DOI:10.1002/app.1988.070350209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractSteady‐state shear rheological properties of liquid crystalline solutions of four ethyl celluloses (ECs) were determined at a low shear rate (1 s−1) and at relatively high shear rates by using two rheometers (cone‐plate and capillary types), and were compared with those of liquid crystalline hydroxypropyl cellulose (HPC). The effect of molecular weight (MW) on the viscoelastic behavior was also determined. The viscoelastic behavior was also determined. The viscometric behavior of EC solutions was similar to that of HPC solutions: (1) with respect to temperature, the shear viscosity (η) at shear rate of 1 s−1exhibited a minimum (ηmin) and a maximum (ηmax), and the concentration–temperature superposition for η could be applied; (2) the behavior of η at relatively high shear rates as a function of shear rate or polymer concentration was typical of lyotropic liquid crystals. The MW dependence of ηminwas greater than that of ηmaxfor EC solutions. The behavior of the elastic parameters such as Bagley correction factor (v), entrance pressure drop (ΔPent), and die swell (B) at relatively high shear rates for EC solutions was essentially similar to that for HPC solutions: (1) the shear rate or stress dependence of the elastic parameters was greatly dependent on whether the polymer solution was in a single phase or biphase; (2) with respect to concentration the elastic parameters showed a maximum and a minimum and the maximum or minimum point for each parameter was not always identical to each other. η for the isotropic or fully anisotropic solutions at a given concentration (C) increased, whereas η for the solutions in the vicinity of the biphasic region showed a minimum, with respect to MW. The slope of η at a given shear rate vs.CMwdepended on shear rate, and this slope for the isotropic solutions appeared to be greater than that for fully anisotropic solutions. ΔPentandvat a given concentration showed either a monotonical increase or a maximum or minimum with MW, and this behavior was not fully consistent with that of η.Bfor the isotropic solutions increased andB's for both biphasic and fully anisotropic solutions were al

ISSN:0021-8995    

DOI:10.1002/app.1988.070350210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY